For preparing a compound of the formula (1) shown below, a process is known in which 3-amino-9-alkylcarbazole of the formula (5) shown below and chloranil are condensed in an inert solvent in the presence of an acid coupling agent to obtain a compound of the formula (2) shown below and this compound is subjected to ring closure using a ring-closing agent (PB Report 65,657, Japanese Patent Post-Exam Publication JP-B-60-11986, etc.). Also, processes such as disclosed in Japanese Patent Unexamined Publication JP-A-54-56630 and JP-A-58-120673 have been proposed for forming a pigment from its crude obtained according to the above process.
This pigment crude, however, is poor in dispersibility and requires strong dispersion for preparation of pigment, so that production efficiency is low and it is difficult to obtain a high-quality pigment from this crude. It has been proposed to pulverize the crude with a surfactant or a coloring matter derivative for a dispersion (JP-A-2-102272, JP-A-2-102273, U.S. Pat. No. 5,275,654, etc.). This method, however, still involves many problems such as low production efficiency, insufficient atomization and poor dispersion stability.